Sn is widely used as plating materials for forming plating films on the surface of metal materials. For example, plated copper materials, in which Sn plating or solder plating is plated on the surface of the copper substrate made of copper or copper alloy, are widely provided as materials for electric components such as lead frame, connector, and the like. In addition, such plated copper materials are used for the semiconductor equipment.
In addition, the Tin materials, in which Sn plating is formed on the steel plate, are used in a variety of applications conventionally.
In Sn plating, there is a problem that characteristics of the plating film change occasionally due to precipitation of impurities in the Sn plating solution with Sn. In addition, the presence of the impurities in the Sn plating solution has a substantial impact on platability. Thus, Sn plating solution with reduced level of impurities is demanded.
In addition, since impurities in the Sn plating solution are accumulated while in use, there is an occasion that platability deteriorates with the passage of time. Thus, efficient removal of the impurities from the used Sn plating solution is required.
Methods of removing Cu as an impurity from non-electrolytic Sn plating solutions are proposed in patent literatures 1-3 (PTLs 1 to 3).